Chamosite after Almandine

Unknown Owner

Sharp large crystals of what were once almandine now replaced by chamosite. These are set up on a small amount of matrix and in great condition. Classic pseudomorph specimen for this area. Collected in April, 1995.The Spurr Mine in Baraga County, Michigan was one of the major iron mines of the Michigamme Range in the Upper Peninsula. Development began in the late 19th century after the discovery of rich iron ore in Precambrian banded iron formation. Underground mining operations extracted hematite ore that supplied iron for the growing steel industry around the Great Lakes. The mine operated for several decades before closing as high grade ore reserves were depleted and iron production shifted to other regions.A pseudomorph is a mineral specimen in which one mineral replaces another while preserving the original crystals external shape. In the case of chamosite after almandine, the original almandine garnet crystal was chemically altered and replaced by chamosite, a chlorite group mineral. The resulting specimen keeps the typical garnet crystal form even though the internal composition has changed. Such specimens are valued because they clearly show the process of mineral replacement while preserving the earlier crystal shape.